This invention relates to a variable-discharge high pressure pump (hereinafter sometimes referred to as "high pressure pump") for supplying a fuel under pressure to a common rail of a diesel engine and also relates to a method of controlling the pump.
Conventional variable-discharge high pressure pumps have a construction for supplying a fuel to a common rail of a diesel engine which construction includes: a plunger; a plunger chamber in which the plunger is movably accommodated; a cam for making the plunger move reciprocatively; an electromagnetic valve which is opened out toward the interior of the plunger chamber; a reservoir which communicates with the plunger chamber through the electromagnetic valve; a check valve which communicates with the plunger chamber and is capable of opening at a predetermined pressure; and an inlet pipe through which the fuel is supplied at a low pressure to the fuel reservoir.
One structural feature of this type of conventional high pressure pump resides in that a part of a low pressure fuel supplied through the inlet pipe is supplied to the reservoir while another part of the low pressure fuel is supplied to the plunger chamber. That is, a fuel inlet which opens into the plunger chamber and an outlet of the plunger chamber through which a part of the fuel is returned to the fuel reservoir are formed separately from each other. If in this high pressure pump the electromagnetic valve malfunctions by being fixed in a closed state, the flow of the fuel ejected through the check valve cannot be controlled. In such an event, there is a risk of the pressure in the common rail abruptly increasing and exceeding a limit pressure determined according to the strengths of the engine and the fuel injector and to the conditions for safety, resulting in damage to the members of the fuel injector.